Chitosan oligosaccharides which are prepared by hydrolyzing chitosan are widely used as edible ingredients essentially in the field of dietary supplements. The starting substance, chitosan generally has N-acetyl groups which partly remain in its sugar residues, and its hydrolysates, oligosaccharides generally have N-acetyl-D-glucosamine residues in addition to D-glucosamine residues.
Such partially-deacetylated chitin oligosaccharides have been reported to have an elicitor activity for plants and have an anticarious activity, and there are known some examples demonstrating that these activities of partially-deacetylated chitin oligosaccharides are higher than those of chitin oligosaccharides and chitosan oligosaccharides having the same degree of polymerization.
However, the substances which are referred to as partially-deacetylated chitin oligosaccharides are generally in the form of mixtures each comprising a plurality of different compounds, and their structures have not as yet been clarified. Therefore, it is very meaningful to provide partially-deacetylated chitin oligosaccharides each having a defined individual structure for the purpose of clarifying the mechanisms of chitin oligosaccharides, partially-deacetylated chitin oligosaccharides and chitosan oligosaccharides as to how they express their various physiological activities.
A report is known in which they say that 2-acetylamino-4-O-(2-amino-2-deoxy-.beta.-D-glucopyranosyl)-2-deoxy-D-gluc ose which is the element unit of a partially-deacetylated chitin oligosaccharide having a defined structure can be produced by decomposing a partially-deacetylated polymer chitin with a chitinase (see Mitsutomi, M. et al., Agric. Biol. Chem., 54 (4) 871-877, 1990). In the reported method, however, hetero-oligosaccharides, of which their structures are very similar to the structure of said compound, are produced as side products along with said compound, and it is very difficult to isolate and purify said compound. For this reason, no one has heretofore tried to isolate said compound to use it as a glucide material in various fields.